1. Field of Invention
This invention relates to a roof mounted solar collector support system with a central post and truss structure with long span capacity that substantially reduces the required roof connections, that is easily deployed to a desired angle of inclination and subsequently tilted to provide access for roofing and other servicing. This field deployable structure has as its main structural elements the employment of a single central support and truss elements that substantially reduce beam bending stress and deflection from applied loads. This long span beam system configuration with its offset central post substantially reduces bending loads that are imparted to the roof due to wind. This invention allows attachment directly to major beam supports below the roof, while only requiring access from above.
2. Prior Art
For many years structural beams have been used to support solar panels as well as other equipment in arrays of various sizes and shapes. The larger or longer span arrays require taller and stiffer structures to withstand the loads and resultant stresses. There have been a number of structures that have become widely used for solar panel applications including the ‘strut’ family of U shaped or double U shaped rolled steel or extruded aluminum structures. In all instances these strut structures have a uniform shape throughout their length. They are often simply supported at or near each end and subject to uniform loading along their length causing excessive bending stresses as the distance from the supports increased. Typically the maximum practical length for roof mounted solar panel support structures has been 4 to 12 feet. Longer spans have been provided but have required increasingly stiffer and more costly structures.
More recently other more unique special shapes have become popular including those that reduce the installation labor required. For commercial applications requiring larger arrays it has become increasingly important to have longer spans that require less anchored support posts to reduce costs for both roof mounted as well as ground mounted systems. However very few commercially available support structures exist that provide long span capability due to the cost of these higher profile structures. And few inroads have been made in devising easily deployed truss-like structures for solar mounting applications.
Some work has been done over the years to develop cost-effective field deployable truss structures for long span applications. Ignash, U.S. Pat. No. 6,321,521, developed a collapsible 3 sided truss structure that allows the three framework sections to be folded together to form the truss beam. Nygren, U.S. Pat. No. 6,076,770, developed an inwardly foldable truss to reduce space for shipment. Merrifield, U.S. Pat. No. 7,028,442, developed a linearly expandable truss structure that allowed variable length structures. And Beltz, U.S. Pat. No. 4,546,591, developed a truss structure with removable pins to allow the structure to be collapsed.
All of the commercially available support struts suffer from a number of disadvantages. For simply supported structures with uniform loads applied throughout their length, maximum bending stress occurs in the center of the beam. Because a beam that is extruded or roll formed has a uniform shape, it will be significantly heavier overall than one that can be varied to have maximum stiffness only where needed. For this reason a continuous profile is relatively heavy as a long span support and therefore not cost-efficient due to its weight to stiffness ratio. This relatively higher weight is also not desirable for rooftop installations where lifting equipment is limited.
Generally the mass of a beam will increase at a faster rate than the rate of increase of the span in order to maintain consistent beam support. For example, if the solar panel support span is doubled in length, the corresponding beam weight will increase by a factor of approximately 3. This is why continuous profile structures have not been economical solutions for large spans. For this reason conventional beams must be supported at relatively closer spacing leading to more supports required.
It is general knowledge that many simply supported structures such as bridges are constructed in a truss shape that concentrates more structural material in the center of the span to withstand the peak moment and prevent excessive stress and sag in the middle of the structure. However this type of structure is difficult to incorporate into cost-competitive products for solar panel support. Efforts to utilize truss structures for supporting PV systems as well as for supporting other equipment have seen only limited use. In most cases the additional field construction labor cost to erect the truss structure has negated their value. Field installation labor costs for truss structures have in some instances far exceeded the cost of the entire truss structure.
Prefabricated truss structures have also been used for solar panel support as well as for supporting other equipment. In these cases the field construction costs are virtually eliminated. However three dimensional prefabricated strut structures are significantly more expensive to build, ship, and stage on a job site. Additionally the expense of bringing these expanded structures to the roof of a building also creates a significant expense. The patent examples described above all have the ability to be folded or collapsed for minimizing shipping space and being deployed once it is delivered on site. However, most expandable structures are comprised of a multitude of components that make them expensive to manufacture—particularly for long span applications.
Another problem associated with long span structures is that they create significantly higher concentrated loads at each connection to the roof. First of all, the lift loads on solar panels in accordance with ASCE structural calculations may be 25 pounds per square foot or higher. This may cause concentrated loads of thousands of pounds at each roof connection point. Furthermore because of the tilted angle required for solar panels this wind load causes a considerable side loading which in turn creates a twisting or bending load at the roof connection point. These factors limit the applicability of long span structures with conventional connection methods. In order to withstand these high loads it is necessary to attach to major structures within buildings. This has not been a simple task since many of the major beam structures in buildings are typically well below the roof surface and therefore difficult to access without going inside the building to secure the connections.
Thus there have been few cost-effective solutions for long span support of solar and other equipment on rooftops and for ground mounting in the 12 feet and greater length range. They typically consisted of either large, massive support beams, or some form of truss structure that was expensive to build, ship and deploy in the field. And solutions have been even more evasive because of the structural and access difficulties associated with high load connections.
In summary, all of the prior art for long span beam support structures suffer the disadvantages noted above including the following:                1. Continuous beam profiles for long spans are expensive due to the cost of the material.        2. Continuous beam profiles are difficult to handle and install because of their resultant excessive weight.        3. Prefabricated truss structures are expensive to build, ship, and install because of their size.        4. The currently available deployable truss structures are complicated, expensive, and require considerable labor to erect in the field.        5. Difficulty of attachment limits the cost-effectiveness and usefulness of currently available long span structures        
The above mentioned disadvantages provide a general background with the prior art devices. The present invention does not suffer the disadvantages noted above but the above discussion provides a way of comparing it with prior art.
In summary there is a need for long span support systems for solar panels that are easily deployable.